1. Technical Field of the Invention
The present invention relates generally to a battery unit which includes a storage battery disposed in a storage case mounted in vehicles such as automobiles.
2. Background Art
Battery units are known which include a storage battery (also called an assembled battery module) equipped with a plurality of electrochemical cells and disposed in a storage case in the form of a battery pack mounted in vehicles such as automobiles. This type of battery units are concerned about being stepped by people at places of installation thereof and thus shaped to improve the mechanical strength thereof. For instance, in the case where the battery unit is mounted in an automotive vehicle, it may be located in a passenger compartment because it is desirable to place the battery unit away from hot environments in terms of characteristics thereof. It is, however, concerned that the battery unit is stepped in error by occupants in the passenger compartment or the occupants mistakenly drop things on the battery unit, thus requiring the battery unit to have a mechanical strength great enough to withstand the external force.
For instance, Japanese Patent First Publication No. 2006-339031 teaches a battery pack which includes a storage battery equipped with a stack of electrochemical cells each covered with laminate films (which will also be referred to as laminated cells or laminated-type cells below). The battery pack also includes a storage case, a cover, and clampers. The storage case has the storage battery installed therein. The storage case has an open end closed by the cover. The cover is pressed by the clamper to hold the storage battery under pressure within the storage case. The storage case is made of metal such as aluminum material which is shaped to have a thickness achieving a desired mechanical strength.
Generally, the stiffness or rigidity of the whole of the storage case is enhanced in order to increase the mechanical strength against the external force. This, however, results in an increased in weight of the battery unit, which is inconvenient for installation thereof in the automotive vehicles.